Patent GB-391861-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/42
Filed: 1931-11-06
Abstract: 391,861. Automatic exchange systems. AUTOMATIC ELECTRIC CO., Ltd., Strowger Works, BELAS, F. T., 27, Arlescourt Road, West Derby, both in Liverpool, and BAKER, G. T., Blackbrook, Caerphilly, Glamorgan. Nov. 6, 1931, No. 30834. [Class 40 (iv).] Selectors for use by toll and other preferential operators are arranged to hunt, if necessary a plurality of times, over the same group of junctions under different testing conditions, these conditions being also modified in accordance with the type of operator employing the selector. The invention is described with reference to a network for a large town comprising automatic local exchanges within the town and manual suburban exchanges. All calls to a suburban exchange are extended through a central toll exchange over a single group of junctions, local calls by a local operator employing a selector, Figs. 3 and 4 (not shown), suburban calls from another suburban exchange by a suburban operator over the selector shown in Figs. 1 and 2, and toll calls from a different area by a toll operator also over the selector of Figs. 1 and 2. When this selector is employed by a suburban operator it may hunt three times testing respectively for an idle junction, a junction engaged in a local call, and a junction engaged in a suburban call but not having another selector waiting on it. When employed by a toll operator, the selector may make four hunting operations testing respec. tively for an idle junction; a junction engaged in a local call, a junction engaged in a suburban call with or without a second selector waiting on it, and a junction engaged in a toll call but without another selector waiting on it. Suburban call. Impulses of the first digit are repeated by relay A to vertical magnet VM in series with C, the release of which at the end of the digit operates relay E so that the impulses of the next digit pass to magnet MM of a single-motion marking switch MS. At the end of this digit relay RC, which was first energized over the normal position of wiper 1a and then held by relay C, releases completing a circuit for the rotary magnet RM which interacts with relay GA. When the first contact of the marked group is reached relay GA remains locked over wiper MRK in series with relay RC which locks to wiper 1a, thereby short-circuiting GA. Relay HS now operates over a bank PBX having a metallic connection for each line of the group and completes on the relapse of relay E a new circuit for magnet RM. Relays C, GA, - E operate temporarily and between the relapse of relays C, E relay H tests the first-junction over wiper P. Hunting takes place until an idle junction is found when H operates earthing wiper P to mark the junction busy and wiper PS to indicate that it is busy in a suburban call. If no idle junction is found, relay HS releases at the end of the group completing a circuit for relay RN which releases RC and closes a circuit for rotary-release magnet RZ to restore the wipers to the beginning of the level. Two-step relay BD operates partially when RN operates and fully when release is complete to connect battery to both test wipers PS, PT: Relay BD also operates relay ST over its upper winding. The wipers are set to the first junction of the group under the control of wiper 2a as before and the switch then hunts again with magnet RM and relay GA interacting, the continuance of the hunting being dependent on the operation of relay ST over its middle or lower winding and earth or booster battery on one of the wipers PS, PT. When a junction engaged in a local call is reached relay ST releases and the subsequent relapse of C, E connects direct earth to wiper P to release the local connection. If no junction engaged on a local call is found, rotary release takes place as before, two-step relay CO operates, releasing BD, and the switch hunts a third time, it now being able to stop on a junction engaged in a suburban connection since relay ST will only operate over its lower winding to continue the hunting if wiper PS encounters booster battery. On the relapse of C, when such a junction is found, relay CR operates, locks to busy earth on wiper P, connects booster battery to wiper PS to indicate that another selector is waiting on the busy junction, and connects an interrupter to the incoming b-wire to inform the operator. In the other selector, relay G operates over the booster battery applied to wiper PS and connects ground to wire DSC to warn the operator to release the junction as soon as possible. When this is done, relay CR releases and H operates to switch through. If the third hunt is unsuccessful the relapse of relays C, E operates G which connects a busy-flash signal .to the b-wire and actuates a meter over wiper P. Toll call. Relay K operates to earth on wire DSC at the toll operator's position. The first two hunting operations take place as in a suburban call but relay BD then remains energized so that wiper PS is completely disconnected whilst PT is connected to battery. During the third hunt, therefore, relay ST will operate to continue hunting only if wiper PT encounters earth or booster battery corresponding to a toll connection without or with a second selector waiting. When a non-toll busy junction is found the test wiper P is earthed as before to release the suburban connection, and if a second selector is waiting this will continue waiting on the toll connection. ' The switching relay H earths wiper PT to mark the junction toll-busy. If the third hunt is unsuccessful rotary release occurs as before, relay BD is released by RN, and a fourth hunt occurs with wiper PT conected to earth over rectifier MRA so that ST will only operate if PT encounters booster battery. If a required junction is found relay CR operates as before and connects booster battery to wiper PT to indicate that the junction is busy with a toll call and has another toll call waiting. If the fourth hunt is unsuccessful relay G operates to give busy-flash and operate a meter as before. Systems using amplifiers. Certain of the junctions of a group may have amplifierswitching facilities. In this case the first of such junctions will be directly reached by dialling an appropriate digit and the switch will hunt only over this sub-group.. When such a junction is reached the operator applies booster battery to the wire RT to operate over wiper P a relay which switches over to an amplifier operator who sets up a direct connection, the connection over the switch being used for supervision only. Junctions employing ring-down clearing. Such junctions are connected to particular levels on which post-springs NP connect resistance earth to lead DSC when the selector switches through to operate a change-over relay which bridges & ring-off relay across the line. A marginal relay in series with the changeover relay is operated by relay G when a second selector' is waiting on the junction to signal this fact to the operator. Release. The release of relay B completes a circuit over wiper 1a for. relay GA which interacts with magnet MM to return MS to normal. The release magnet ZM of the main selector is then operated over wiper 1a. During release the selector is marked busy over contacts of relay C operated in series with magnet MM and over contacts ZM of the release magnet. Local call. The selector employed is in general similar to that of Figs. 1 and 2, but without the repeated-hunting provision, and without the marking switch MS the second digit passing directly to the rotary magnet.